Measurement Computing WBK Options - Manual (Page 70)

WBK16, pg. 30 949794 WBK16, Strain-Gage Module
2 Point Manual Calibration
In the 2 Point Manual Calibration method two readings are taken from the gage with different loads applied for each
reading. For this method, the user must enter the following 5 parameters:
Excitation - The value of the constant voltage source used to excite the gage.
Max Load - The maximum load value the gage is expected to measure. This value could be less than the
max rated load of the gage.
Quiescent Load - The minimum load value the gage is expected to measure. This value could be greater
than the min rated load of the gage.
Point 1 Units -The load that will be placed on the gage for the first calibration measurement.
Point 2 Units - The load that will be placed on the gage for the second calibration measurement.
Example: Excitation voltage is set to 10 volts. A strain gage with a full load rating of +/- 1000 µe is connected to
a StrainBook [or WBK16] channel. However, the gage will be used in an environment were the expected range of
measurement is limited to 0 to 600 µe. Two certified loads of 50 µe and 500 µe are available for calibration. In
the Calibration Parameters spreadsheet, the user would enter the values as follows:
Excitation = 10V
Max Load = 600
Quiescent Load = 0
Point 1 Units = 50
Point 2 Units = 500
1. When the > toolbar button is pressed, the user is prompted to load the gage
with 50 µe.
2. After the load is applied, and the button pressed, WaveView takes several voltage readings in an
attempt to find the best gain setting for the first load value.
3. When finished, the user is prompted to load the gage with 500 µe.
4. After the load is applied, and the button pressed, WaveView again takes several measurements to
find the best gain settings for the second load value.
5. After both voltage measurements are obtained, WaveView configures the input channel to provide the
optimum settings for the two amplifier gain stages, and the Offset DAC. WaveView also sets the
channels mX+b parameters for proper conversion of the input voltage measurements to units of µe (or
whatever units have been specified by the user).
Note: The greatest accuracy is obtained from 2 Point Manual calibration when the two calibration points are at the
min and max load range of the gage. In the above example, the greatest possible accuracy would be
obtained if Point1 was equal to the Quiescent load, and Point 2 was equal to the Max load.
2 Point Auto Calibration
For 2 Point Auto Calibration the user must enter the following 7 parameters:
Excitation - This is the value of the constant voltage source used to excite the gage.
Max Load - Is the maximum load value that the gage will be expected to measure. This value could be
less than the max rated load of the gage.
Quiescent Load - Is the minimum load value that the gage will be expected to measure. This value could
be greater than the min rated load of the gage.
Point 1 mV - This is the output voltage generated by the gage at the Point 1 Units load.
Point 1 Units - This is the load that is associated with the Point 1 millivolt value.
Point 2 mV - This is the output voltage generated by the gage at the Point 2 Units load.
Point 2 Units - This is the load that is associated with the Point 2 millivolt value.
No actual readings are taken when a 2 Point Auto Calibration is performed. Calibration constants are calculated
from the values entered by the user.